DSA (Digital Subtraction Angiography) and other angiographic tests based on computer images are being used for diagnosis of vascular and tumorous diseases. In such angiographic tests, in inserting a catheter from a puncture hole in a blood vessel into a target artery, the front end of the catheter must be freely moved in the direction of travel and along curves by applying an external force on the hand side in a remote control fashion.
In recent years, it has been required to perform not only a selective operation for inserting a catheter into a primary branch of the aorta but also a super-selective operation for inserting a catheter into secondary and tertiary branches of said primary branch. Thus, a higher technique and rich experience have become indispensable for said remote control.
To secure the remote controllability (torque controllability), it has been common practice to resort to selection of a material for catheters.
That is, if such material of a catheter is soft (highly flexible), it is difficult to effect remote control on the hand side. Thus, as suggested by Japanese Utility Model Application Laid-Open Specification No. 500013/1985 (International Application PCT/US 83-864) and Japanese Patent Application Laid-Open No. 218966/1983, excluding a predetermined short region on the front end side where softness is required in view of stability of a catheter, the entire portion on the hand side is reinforced by steel wire mesh or is constructed in the form of a double tube made of materials having different entire portion on the hand side is rigid with reduced flexibility, thereby giving torque controllability to the catheter.
Making catheters slender is an adverse factor for said torque controllability, making it difficult to secure safety for remote control. For this reason, there has not been established an operating method for inserting a catheter through a puncture hole in the brachial artery, which is thin and long, for angiographic tests; at present, angiographic tests with respect to the general artery are conducted by inserting a catheter through a puncture hole in the femoral artery, which is thick.
However, it may be said that said controllability for catheters with respect to blood vessels can be secured by simultaneously using a catheter introducing guide wire which is highly flexible and which will not form a fixed bend (a so-called bending habit) even if subjected to an operating external force, said guide wire being inserted into a catheter and operated for piloting the catheter. In other words, unlike the technique resorting to the selection of a material for catheters, this idea is to look to a guide wire for torque controllability and, as it were, to reflect the controllability of the guide wire on the catheter.
In the case where such special technique is adopted, if the entire portion on the hand side is made rigid as by double-tube construction or steel wire mesh, this arrangement will destroy the superior flexibility that the guide wire possesses.
That is, in inserting a catheter into a puncture hole in the brachial artery, since, anatomically, the region extending from the sub-clavian artery via the aortic arch to the downwardly extending artery is sharply bent at less than 90 degrees, the catheter, even if made rigid, will form a corresponding bending habit under the action of body heat.
Further, in inserting a catheter into a puncture hole in the femoral artery, if this artery is abnormally bent or deformed owing to severe arteriosclerosis, the catheter inserted therein is heated by body heat and forms a bending habit corresponding to such abnormal bend.
As a result, the guide wire expected to guide the catheter correctly is "defeated" by the catheter and its inherent torque controllability is impaired, so that the catheter cannot be correctly operated until it reaches the target artery. Further, the more rigid the catheter material, the more strongly the catheter is urged against the blood vessel wall when it is retained in the blood vessel. As a result, the danger of formation of a thrombus or occlusion of blood vessel taking place increases.
In brief, when it is desired to utilize the torque controllability of a guide wire to be used for remote-controlling a catheter, it is preferable that the main portion of the catheter be made soft with high flexibility, since this makes it possible to precisely reflect the free movement of the catheter introducing guide wire; thus, the performance of the guide wire can be efficiently and reasonably developed.
On the other hand, a catheter is a medical instrument for injecting a contrast agent into a target artery. If, however, its front end portion is made soft with high flexibility, as in the known example described above, the front end portion of the catheter is subjected to the pressure under which the contrast agent is injected, swinging to and fro, with the result that the control agent cannot be injected into the target artery correctly and without loss and concentratedly. In this connection, even if a superior DSA apparatus by which target locations can be graphically represented with diagnostic contrast agent, there would be the danger of said contrast agent being misdirected.
In the case where it is desired to effect plastic working to provide an intrinsic bend suitable for the primary, secondary and tertiary branches of the artery so as to provide the front end portion of the catheter with the pilot function for inserting the catheter into a blood vessel, the softer the front end portion, the more difficult it is to form such bend in a stable manner.
Thus, so long as the above-described technique of inserting and operating a catheter to be used simultaneously with a guide wire is adopted, it is preferable that the front end portion of the catheter have the necessary minimum of rigidity (low flexibility). It goes without saying that the necessary minimum means a degree which does not hurt the blood vessel wall nor impair the torque controllability of the guide wire. It appears that a catheter for angiography meeting the necessary conditions described above has not been developed yet.